In a modern high building construction site, a derrick is often utilized to hoist heavy articles, for example, steel beams, to a desired location. However, the conventional derrick has disadvantages that since its counterweight is fixed in position and has a fixed weight, a loading of the heavy articles hoisted by the derrick cannot be effectively balanced by the counterweight, which causes that a frame of the derrick must have a very strong structure. This means that the parts constituting the frame should have a large size or be made by steel having a high strength which correspondingly means that these parts involve a high cost.
Furthermore, since the loading cannot be balanced, an unbalanced force will act on a bearing of a boom of the derrick, which causes the bearing to be damaged very easily.
Moreover, the conventional derrick cannot provide a secure manner which can ensure that the load the derrick is preparing to hoist will not exceed the rating loading that the conventional derrick is designed to hoist.
Finally, when the conventional derrick starts hoisting an article, it will always apply a sudden large hoisting force on the article or container of the article for the hoisting operation. Such an application of a sudden large force will cause a damage to the article or the container thereof.
The present invention is disclosed to obviate/mitigate the above mentioned disadvantages of the conventional derrick.